Extremophile

An extremophile is an organism, usually unicellular, which thrives in or requires "extreme" conditions. It is important to note that the definition of "extreme" in this context is anthropocentric; from the point of view of the organism, its environment is completely normal.

Types of extremophiles

There are many different classes of extremophiles, each corresponding to the way its chosen environment differs from what is considered "normal" by other organisms. These classifications are not exclusive. Many extremophiles fall under multiple categories. For example, organisms living inside hot rocks deep under Earth's surface are both thermophilic and barophilic.

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• Acidophile: An organism with an optimum pH level at or below pH 3.
• Alkaliphile: An organism with optimal growth at pH levels of 9 or above.
• Endolith: An organism that lives inside rocks.
• Halophile: An organism requiring at least 0.2M of NaCl for growth.
• Hypolith: An organism that lives inside rocks in cold deserts.
• Metalotolerant: capable of tolerating high levels of heavy metals, such as copper, cadmium, arsenic, and zinc.
• Oligotroph: An organism capable of growth in nutritionally limited environments.
• Piezophile: An organism that lives optimally at high hydrostatic pressure. See also Barophile
• Psychrophile: An organism that can thrive at temperatures of 15 °C or lower.
• Radioresistant: resistant to high levels of ionizing radiation.
• Thermophile: An organism that can thrive at temperatures between 60-80 °C.
• Xerotolerant: requires very little water to survive.